Step stool



FIG. 1 is a front, right, top perspective view of a step stool showing my new design;

FIG. 2 is a rear, left, top perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a left side view thereof; and,

FIG. 7 is a top view thereof. 

CLAIM The ornamental design for a step stool, as shown and described. 